The disclosure relates to a cylinder liner for a cylinder of an internal combustion engine
The task of the cylinder liner is to minimize wear in its function as a frictional partner to the piston rings, to dissipate the heat of combustion and to improve the mechanical stability of the system during operation while minimizing operationally caused distortion. A distinction is made between wet and dry cylinder liners, depending on their function.
Wet cylinder liners have a collar via which the cylinder liner is fixed in the vertical direction in the engine block, or cylinder housing. The rotationally symmetrical outer contours of the cylinder liner, including the collar, determine a minimum cylinder spacing. Wet cylinder liners are pushed into the cylinder housing into suitably machined seats. Seal rings are used to seal against coolant and oil. Previous wet cylinder liners are normally produced by centrifugal casting and then machined rotationally symmetrically. In the case of wet cylinder liners that are cooled from outside using a coolant, thermal and mechanical stresses can cause cavitation or corrosion damage on the surfaces contacted by the coolant, which can endanger the operation of the engine, depending on its extent. In this cavitation effect, air bubbles formed in the coolant by excitation implode and erode the outside of the liner, where the vibration of the cylinder liner can magnify the erosion.
Dry cylinder liners are pressed, shrunk or cast into the cylinder housing. The water jacket, in contrast to wet cylinder liners, is not located between the liner material and the cylinder housing but is a component of the cylinder housing casting, as with monometallic construction. Dry liners are produced from cast iron, aluminum alloys or as sintered liners from powdered metal materials.
For protection against cavitation, DE 10 2006 042 549 A1 reveals a rotationally symmetrically shaped wet cylinder liner that is given a protective coating on the outside. For this purpose, at least the outer surface areas of the iron-based alloy cylinder liner contacted by the coolant are coated with a thermal sprayed coating.
In order to minimize wear from cavitation it is further known to include additives in the coolant that have a positive effect on the steam pressure of the coolant. The disadvantage is that this measure requires increased maintenance expense to replenish the additives or to check the mixture ratio. A further proposal relates to using cylinder liners of a material with a high module of elasticity, for which a more cost-intensive vermicular graphite cast iron or steel, for example, is proposed as an alternative to cast iron as the material.
DE 196 05 946 C1 reveals a manufacturing process for cylinder liners with which a liner with a thin wall thickness is produced initially to achieve improved wear resistance. A mandrel having an outside diameter corresponding to the inside diameter of the cylinder liner to be produced is used as the mold, and a sprayed material of the desired thickness is applied to the outer peripheral surface of the rotating mandrel, using a known thermal spraying process. Then the liner on the mandrel can be ground and shaped if necessary. After being removed from the mandrel, the liner is machined on its end faces if this is required.
The cylinder liner from DE 195 78 11 A1 consists of two different materials. A liner insert of cast iron is surrounded on the outside by a carrier cylinder made of steel. This known concept using two components arranged concentrically to each other involves high manufacturing costs and, therefore, for economic reasons is not considered for use in series mass production.